CN101835314B

CN101835314B - LED drive circuit with dimming function and lamp

Info

Publication number: CN101835314B
Application number: CN2010101762470A
Authority: CN
Inventors: 邝乃兴; 杜磊; 张军明; 任远程
Original assignee: Monolithic Power Systems Inc
Current assignee: Monolithic Power Systems Inc
Priority date: 2010-05-19
Filing date: 2010-05-19
Publication date: 2013-12-04
Anticipated expiration: 2030-05-19
Also published as: CN103313472A; EP2389046A2; EP2389046A3; CN101835314A; US8581518B2; US20110285301A1; CN103313472B

Abstract

The invention discloses an LED drive circuit with dimming function and a lamp. The LED drive circuit comprises a TRIAC dimmer; the TRIAC dimmer receives an alternating-current input voltage and generates a cut phase voltage signal; the cut phase voltage signal is rectified by a rectifying module and then coupled to a dimming signal generator; and a power factor correcting controller receives an output signal of the dimming signal generator, reflects a feedback signal of LED brightness, and outputs a switching control signal to control the on and off of a switching tube so as to drive an LED. The dimming of the LED is implemented by adjusting a conduction angle of the TRIAC dimmer.

Description

A kind of LED drive circuit and light fixture with dimming function

Technical field

Embodiments of the invention relate to a kind of LED drive circuit, relate in particular to and utilize triode ac switch (TRIAC) LED to be carried out to the drive circuit of light modulation.Embodiments of the invention also relate to the light fixture that uses this drive circuit.

Background technology

Triode ac switch (TRIAC) is the rectifying device commonly used of field of power electronics, and the control signal by gate pole can realize its conducting on both direction.After the TRIAC conducting, the gate pole control signal is effect out of hand just, and when the electric current by TRIAC, lower than maintaining electric current, TRIAC becomes cut-off by conducting.

Dimmer based on TRIAC is widely used in the dimmer application to pure resistive loads such as incandescent lamp and Halogen lamp LEDs at present, basic principle is the angle of flow that TRIAC is controlled in the triggering by controlling TRIAC constantly, and then realize the adjusting to light source (load) voltage, reach the purpose of light modulation.

Light-emitting diode (Light Emitting Diode the is called for short LED) advantages such as volume is little, energy-conservation owing to having, long service life, become one of most potential alternative source of light of conventional light source (as incandescent lamp).The light regulating technology commonly used of LED has PWM light modulation and simulation light modulation at present, and the former light modulation principle is to control the ON time of the LED electric current of flowing through, and the latter's light modulation principle is directly to control the size of the LED electric current of flowing through.When adopting TRIAC light modulation scheme, because LED driver is not pure resistive load, can cause by the electric current of TRIAC uncontrollablely because of the LC resonance in circuit, make and can not effectively carry out light modulation.Prior art addresses this problem by the method that increases dummy load (dummy load), but because the power consumption of dummy load has reduced efficiency.

Therefore need to improve the TRIAC light modulation scheme of existing LED, to reduce power consumption, raising efficiency.

Summary of the invention

The objective of the invention is to propose a kind ofly can carry out to LED the drive circuit of light modulation, to solve existing TRIAC dimmer, can not directly apply to LED drive circuit to realize the problem to the LED light modulation.

In one aspect of the invention, proposed a kind of drive circuit that LED is carried out to light modulation, having comprised: the triode ac switch dimmer receives AC-input voltage and generates cut voltage; Rectification circuit is direct current signal by described cut voltage commutation; Filter circuit, described direct current signal is coupled to filter circuit, and filtered signal is coupled to LED through energy transmission; The dim signal generator, receive the signal of the described direct current signal of a reflection; Equivalent load average current computing module, the signal of the signal based on reflection transformer primary side electric current and embodiment switching tube state generates the signal (506) of reflection LED brightness, and the signal (506) of described reflection LED brightness is proportional to the current average of the LED that flows through; And power factor correction controller, receiving the output signal of dim signal generator and the signal of reflection LED brightness, output switch control signal is with the control switch pipe.

Preferably, described power factor correction controller is APFC.

Preferably, described power factor correction controller works in critical conduction mode.

Preferably, described power factor correction controller works in continuous conduction mode.

Preferably, described power factor correction controller works in discontinuous conduction mode.

Preferably, described energy transmission is transformer.

Preferably, described energy transmission is inductance.

Preferably, described drive circuit is based on any in forward topology, flyback (FLYBACK) topology, half-bridge (HALF-BRIDGE) topology, push-pull topology.

Preferably, described drive circuit is based on any in step-down (BUCK) topological structure, (BOOST) topological structure that boosts, buck (BUCK-BOOST) topological structure, single ended primary induction transducer (SEPIC) topological structure.

Preferably, the signal of described embodiment switching tube state comes from the output signal that switching tube drives signal or auxiliary winding.

Preferably, described equivalent load average current computing module comprises: the first switch, and an end is coupled to the signal of reflection primary current; Electric capacity, be coupled between the other end and ground of the first switch; Second switch, an end is coupled to the tie point of the first switch and electric capacity; The 3rd switch, be coupled between the other end and ground of second switch; The signal of the tie point output reflection LED brightness between second switch and the 3rd switch; Embody signal controlling the first switch, second switch and the 3rd switch of switching tube state.

Preferably, the combination that described filter circuit comprises any one or capacity cell and inductance element in capacity cell or inductance element.

Preferably, described dim signal generator is according to the controlled signal of cut Voltage-output parameter after rectification.

Preferably, the controlled signal of described output parameter is pulse width modulating signal or amplitude controlled signal.

In another aspect of this invention, proposed a kind of light fixture, this light fixture possesses drive circuit as above.

Above-mentioned drive circuit and use the light fixture of this circuit, solved the TRIAC dimmer existed in the prior art and can not directly to LED, carry out the problem of light modulation, the compatible light modulation scheme of existing conventional light source (as incandescent lamp).

The accompanying drawing explanation

Fig. 1 is the existing technical scheme of TRIAC dimmer to the LED light modulation of utilizing.

Fig. 2 samples for the secondary according to the embodiment of the present invention and the specific embodiment based on multiplier PFC.

Fig. 3 is the waveform of middle coherent signal embodiment illustrated in fig. 2 within the half period of AC-input voltage AC.

Fig. 4 samples for the secondary according to the embodiment of the present invention and the specific embodiment based on conducting duration control circuit PFC.

Fig. 5 samples for the former limit according to the embodiment of the present invention and the specific embodiment based on multiplier PFC.

The concrete block diagram that Fig. 6 is the computing module of equivalent load average current shown in Fig. 5 570.

Fig. 7 samples for the former limit according to the embodiment of the present invention and the specific embodiment based on conducting duration control circuit PFC.

Embodiment

Below in each specific embodiment and accompanying drawing, unless emphasized in addition, identical mark represents identical part.

Fig. 1 is existing LED triode ac switch (TRIAC) light modulation scheme schematic diagram.The following describes its light modulation principle.AC-input voltage Vin is after the effect of TRIAC dimmer, the constantly controlled voltage signal 101 of output conducting, obtain unidirectional voltage 102 through rectification module again, obtain voltage 103 after voltage 102 dividing potential drops and flow to the dim signal generator, obtain the pulse signal (pwm signal) 104 that width is conditioned.By regulating the conducting moment of TRIAC dimmer, input voltage 103 waveforms of dim signal generator are changed, correspondingly the pulse duration of the output signal 104 of dim signal generator is conditioned, again through not thering is power factor emendation function (non power factor correction, abbreviation Non-PFC) after the effect of controller, make the energy that is sent to load LED through transformer TR be conditioned, the final control realized LED brightness.

The existence of dummy load in Fig. 1 (dummy load) Rd, can solve because of cause the flowing through electric current I tr of TRIAC dimmer of LC resonance in circuit uncontrollablely, and then causes that the TRIAC dimmer turn-offs uncontrollable and problem that can not light modulation constantly.But then, the introducing of dummy load Rd has produced extra power consumption, and this problem is for becoming more outstanding today of day by day focusing on LED drive circuit efficiency.

The schematic diagram that Fig. 2 is the drive circuit of a specific embodiment according to the present invention, the drive circuit of this embodiment is based on flyback (FLYBACK) topology, the feedback signal sampling, from the transformer secondary, is sampled signal for embodying the signal of LED brightness, as voltage signal or current signal.This embodiment is to have adopted the controller of (power factor correction the is called for short PFC) function that has power factor correction with respect to the improvement of prior art shown in Fig. 1, and has save dummy load Rd.In this embodiment, pfc controller 250 can work in critical conduction mode (critical conduction mode).

Fig. 3 is the waveform of coherent signal within one and half work periods of AC-input voltage Vin in drive circuit embodiment illustrated in fig. 2.3a in Fig. 3 is depicted as AC-input voltage Vin waveform in Fig. 2, and this voltage obtains cut voltage 201 after the TRIAC dimmer, then, after the rectification module rectification, obtains direct voltage 202, and waveform is as shown in the 3b in Fig. 3.β 1 means TRIAC dimmer conduction angle corresponding to this DC voltage waveform, controls the TRIAC dimmer and can realize the control to the angle of flow.

Direct voltage 202 is coupled to transformer through filter circuit 220 on the one hand, obtains voltage 203 through dividing potential drop on the other hand, and waveform is as shown in the 3c in Fig. 3.In this embodiment, this filter circuit comprises capacitor C 1.Voltage 203 is coupled to dim signal generator 230, and the effect of dim signal generator 230 for example is, according to the controlled signal of input voltage 203 output parameters, the controlled or amplitude controlled signal of duty ratio.After filtering the filtered signal of circuit 220 through transformer coupled to LED.

In the present embodiment, dim signal generator 230 comprises comparator 231, and its in-phase end and voltage 203 couple, and end of oppisite phase and signal 204 couple, and dim signal generator 230 output signals 205 couple with pfc controller module 250.In the present embodiment, signal 204 is 0V, and when voltage 203, higher than 0V, output signal 205 is high level, and when voltage 203 values, lower than 0V, output signal 205 is low level.Signal 205 waveforms are as shown in the 3d in Fig. 3.

Pfc controller 250 comprises error amplifier 251, multiplier 252, comparator 253, current zero crossing detector 254, rest-set flip-flop 255.The output 205 of the in-phase end of error amplifier 251 and dim signal generator couples, and end of oppisite phase is coupled with the feedback signal 206 of reflection lamp brightness, and the output signal 207 of error amplifier 251 flows to multiplier 252.Another road of multiplier 252 is input as voltage 203, and the output 208 of multiplier is as shown in the 3e in Fig. 3.Output signal 208 flows to the end of oppisite phase of comparator 253 as the reference signal, the in-phase end of comparator 253 couples with the voltage signal 209 of reflection transformer TR primary current Ip size.The Energy Transfer situation of 254 pairs of transformers of current zero crossing detector is detected, output signal 211.Comparator output signal 210 is to the reset terminal of rest-set flip-flop 255, and the set termination of rest-set flip-flop is received the output signal 211 of current zero crossing detector 254.The output of rest-set flip-flop and switching tube Sw couple, the closed and shutoff of its output signal 212 control switch pipe Sw.As mentioned above, multiplier 252 multiplies each other signal 203 and 207, obtains reference signal 208, makes 208 waveform similar to 203, finally makes primary current Ip peak envelope line similar to signal 203.

When switch S w closure, transformer TR primary current Ip continues to increase, when electric current increases to voltage signal 209 and reaches the reference level value of comparator 253 end of oppisite phase, the output signal 210 of comparator 253 becomes high level, trigger 255 is reset, output signal 212 becomes low level, on-off switching tube Sw, energy is exported to load LED by transformer secondary winding L s afterwards, secondary current Id reduces gradually, when it is reduced to 0, the output signal 213 that this information exchange overcurrent zero-crossing detector 254 detects transformer tertiary winding Lt obtains.Current zero crossing detector 254 output signals 211 are set trigger 255, and trigger output signal 212 becomes high level, again Closing Switch pipe Sw.

3e in Fig. 3 shows the waveform of coherent signal when Rp=1 Ω, and the waveform of electric current I p peak envelope line is the waveform of signal 208.It should be noted that, the 3e in Fig. 3 has just schematically provided several waveforms of electric current I p.The present embodiment middle controller 250 works in critical conduction mode, and secondary current is reduced to 0 rear primary current Ip and increased again at once, until signal 209 rises to reference level.For the purpose clearly demonstrated, the current signal be present in figure between two current waveforms is not shown.

Due to the multiplier output signal 208 as with reference to signal and multiplier input signal 203 waveform similarities, thus the peak envelope line of electric current I p also with voltage 203 waveform similarities.Electric current I p is through capacitor C 1 filtering, and the input current Itr waveform obtained is as shown in the 3e in Fig. 3.Input current Itr waveform is the 201 waveform homophases and similar of the cut voltage after the TRIAC dimmer to AC-input voltage AC, therefore in the situation that do not need to add dummy load, can prevent by mistake being turn-offed of TRIAC dimmer, also improve in addition the power factor of system.

Illustrate that in conjunction with Fig. 3 the TRIAC dimmer realizes the principle of light modulation to LED.

The half period of input ac voltage Vin of take is example, regulates the TRIAC dimmer, makes dimmer conduction constantly from T1, be adjusted to T2, and correspondingly, TRIAC dimmer conduction angle is adjusted to β 2 from β 1.Like this, the angle of flow that the conducting duration of voltage 203 is corresponding is adjusted to β 2 by β 1, and the angle of flow corresponding to output signal 205 high level durations of dim signal generator is adjusted to β 2 by β 1.In two kinds of situations, the waveform of output signal 208 is as shown in the 3e in Fig. 3.During with angle of flow β 1, compare, the angle of flow passes to load energy while being β 2 reduces, and reaches the purpose of light modulation.

Feedback signal 206 samplings are from embodying voltage or the current signal that load LED brightness is relevant, and generation after feedback network 270 effects.Feedback signal 206 is coupled to PFC controller 250, plays the effect of stablizing LED brightness.In the present embodiment, as increased suddenly when LED brightness, the feedback signal 206 that embodies brightness becomes large, and the output 207 of operational amplifier 251 diminishes, and the output 208 of multiplier diminishes, and electric current I p peak value diminishes, and the energy that is delivered to LED diminishes, and LED brightness reduces.

Fig. 4 is the schematic diagram of the drive circuit of another specific embodiment according to the present invention.The drive circuit of this embodiment is that with respect to difference embodiment illustrated in fig. 2 PFC controller 450 does not adopt multiplier, but adopts conducting duration controller (on time controller).

In the situation that AC-input voltage Vin waveform, TRIAC dimmer conduction angle and feedback signal 206 amplitudes are all certain, operational amplifier 251 output signals 207 are a fixed value.Reduce to zero when current zero crossing detector 254 detects secondary current Id, output signal 211 makes rest-set flip-flop 255 set, control switch pipe Sw closure.Under the effect of signal 211 and operational amplifier 251 output signals 207, conducting duration controller 453 is after the duration of a correspondence, and output reset signal 410 is given rest-set flip-flop, output signal 412 on-off switching tubes.

With reference to the 3b in figure 3, the half period waveform of 50Hz civil power AC-input voltage Vin of take is example.The frequency of voltage 202 is 100HZ, and the switching tube operating frequency is high frequency (tens of KHZ is to number MHZ), in the situation that the switching tube operating frequency far away higher than voltage 202 frequencies, supposes that switching tube is in T3 conducting constantly, the peak I pk expression formula of primary current Ip is:

Equation (1)

Wherein, V _T3For the value of T3 moment voltage 202, the switching tube conducting duration that Ton is conducting duration controller 453 correspondences.In the situation that output signal 207 is a fixed value, the Ton duration is a constant, the peak value of electric current I p and V _T3Proportional, so in whole half period waveform, the envelope of electric current I p peak value and voltage 202 waveform similarities.Through capacitor C 1 filtering, input current Itr waveform and voltage 201 waveform similarities, reached the control to input current Itr waveform.

By controlling the light modulation angle of TRIAC dimmer, the duty ratio of dim signal generator 230 output signals 205 is changed, amplifier 251 output signals 207 are controlled the conducting duration of conducting duration controller 453, this conducting duration is the conducting duration of switching tube Sw in a switch periods, make the peak value size of transformer primary side electric current I p be under control, the energy that passes to load LED by transformer is under control, and has realized the light modulation of LED.

Fig. 5 is the drive circuit of another specific embodiment according to the present invention.The drive circuit of this embodiment is to have adopted former limit to control with respect to difference embodiment illustrated in fig. 2.Embody the voltage signal 209 of transformer TR primary current information except being fed to pfc controller 250, also be fed to equivalent load average current computing module 570, another road input of module 570 comes from the output signal 212 of pfc controller 250, and output signal 506 is coupled to pfc controller 250.

The schematic block diagram that Fig. 6 is the computing module of equivalent load average current shown in Fig. 5 570, it comprises: the first switch S 1, the one end is through LEB(lead-edge-blanking circuit) be coupled to voltage signal 209, the other end is coupled to the tie point of second switch S2 and capacitor C 2; Capacitor C 2, be coupled between an end and ground of the first switch S 1; Second switch S2, an end is coupled to the tie point of the first switch S 1 and capacitor C 2, and the other end and the 3rd switch S 3 couple; The 3rd switch S 3, be coupled between the end and ground of second switch S2.Signal 212 is controlled the first switch S 1, second switch S2 and the 3rd switch S 3 simultaneously, the tie point output signal 506 between second switch S2 and the 3rd switch S 3.

When signal 212 is high, i.e. switching tube SW conduction period, second switch S2 turn-offs; The first switch S 1 closure, capacitor C 2 is recharged; The closed ground connection of the 3rd switch S 3, signal 506 values remain zero.When primary current reaches peak I pk, the corresponding maximum Ipk * Rp that reaches of capacitor C 2 both end voltage.Afterwards, signal 212 becomes low, and switching tube SW is turned off, and the first switch S 1 and the 3rd switch S 3 are turn-offed, and second switch S2 closure, make the voltage at capacitor C 2 two ends be coupled output.This state remains to next cycle switch pipe SW by conducting again.

If switching tube SW conducting duration is Ton, the shutoff duration is Toff, and the transformer primary secondary coil turn ratio is N, and the mean value Ieq of signal 506 and the mean value Io of load current can be expressed as respectively:

Equation (2)

Equation (3)

Wherein,

Mean value for secondary current Id.By above-mentioned two formulas, obtain

Equation (4)

Equation (3) illustrates that the mean value Ieq of signal 506 is proportional to load current mean value Io, and signal 506 can the reflected load state, has realized having reached the monitoring to load condition by the former side information of sampling.

In another embodiment, the signal of controlling the first switch S 1, second switch S2 and the 3rd switch S 3 also can come from the signal that other embody switching tube SW state, as the output signal 213 of tertiary winding Lt.

Fig. 7 is the drive circuit of another specific embodiment according to the present invention.The drive circuit of this embodiment is to have adopted former limit to control with respect to drive circuit difference embodiment illustrated in fig. 4, pfc controller 450 realize that principle is with embodiment illustrated in fig. 4 identical, at this in repetition; Be that with respect to drive circuit difference embodiment illustrated in fig. 5 pfc controller 450 does not adopt multiplier, but adopt conducting duration controller (on time controller), what former limit was controlled realizes that principle, with embodiment illustrated in fig. 5 identical, no longer repeats at this.

It should be noted that described embodiment should be construed as explaining and unrestricted the present invention.Without departing from the scope of the invention, those skilled in the art can design many replacement schemes.For example, although described embodiment is all based on the flyback topology, but the present invention is equally applicable to other topological structures in Switching Power Supply, as voltage-dropping type (BUCK), booster type (BOOST), buck-boost type (BUCK-BOOST), single ended primary induction transducer (SEPIC) type, normal shock type, bridge-type, semi-bridge type, push-pull type etc.For another example, although the pfc controller in described embodiment is critical conduction mode, the present invention is equally applicable to DCM (Discontinuous Conduction Mode) or continuous conduction mode (Continuous Conduction Mode).The concrete numerical value of the signal type provided in described embodiment or signal can occur with the form of other types or other concrete numerical value in other embodiments.And for example, according to other embodiments of the invention, filter circuit 220 also can comprise the combination of inductance element or capacity cell and inductance element.And the dim signal generator also can further comprise the RC circuit module, to obtain the controlled parameter of output amplitude.In addition, LED drive circuit as above can be used as independently device and realizes, also can realize in light fixture.

Above content only relates to preferred embodiment or embodiment, can produce many modifications and does not break away from the spirit and scope of the present invention that claims propose, and should not be construed as limiting the scope of the present invention.The described specific embodiment of this specification is only for illustration purpose, and those skilled in the art, in spirit of the present invention and principle, can draw multiple modification, equivalent.The protection range that the present invention is contained is as the criterion with appended claims.Therefore falling into whole variations in claim or its equivalent scope and remodeling all should be the claim of enclosing and contains.

Claims

1. the LED drive circuit with dimming function comprises:

Triode ac switch (TRIAC) dimmer, receive AC-input voltage and generate cut voltage (201);

Rectification circuit is direct current signal by described cut voltage commutation;

Filter circuit, described direct current signal is coupled to filter circuit (220), filtered signal through transformer coupled to LED;

Switching tube, be coupled to the former limit of described transformer;

Dim signal generator (230), receive the signal of the described direct current signal of a reflection;

Equivalent load average current computing module, the signal of the signal based on the described transformer primary side electric current of reflection and the described switching tube state of embodiment generates the signal (506) of reflection LED brightness, and the signal (506) of described reflection LED brightness is proportional to the current average of the LED that flows through; And

Power factor correction (PFC) controller, receive the output signal (205) of dim signal generator (230) and the signal (506) of reflection LED brightness, and output switch control signal (212 or 412) is to control described switching tube.

2. drive circuit as claimed in claim 1, is characterized in that described power factor correction (PFC) controller is APFC.

3. drive circuit as claimed in claim 1 or 2, is characterized in that described power factor correction (PFC) controller works in critical conduction mode.

4. drive circuit as claimed in claim 1 or 2, is characterized in that described power factor correction (PFC) controller works in continuous conduction mode.

5. drive circuit as claimed in claim 1 or 2, is characterized in that described power factor correction (PFC) controller works in discontinuous conduction mode.

6. drive circuit as claimed in claim 1, based on any in forward topology, flyback (FLYBACK) topology, half-bridge (HALF-BRIDGE) topology, push-pull topology.

7. drive circuit as claimed in claim 1, the signal that it is characterized in that described embodiment switching tube state comes from the output signal of the auxiliary winding of the driving signal of described switching tube or described transformer.

8. drive circuit as claimed in claim 1 is characterized in that described equivalent load average current computing module comprises:

The first switch (S1), an end is coupled to the signal of the primary current of the described transformer of reflection;

Electric capacity (C2), be coupled between the other end and ground of described the first switch (S1);

Second switch (S2), an end is coupled to the tie point of described the first switch (S1) and electric capacity (C2);

The 3rd switch (S3), be coupled between the other end and described ground of described second switch (S2);

The signal (506) of the described reflection of the tie point output LED brightness between described second switch (S2) and described the 3rd switch (S3);

Described the first switch of the signal controlling of described embodiment switching tube state (S1), described second switch (S2) and described the 3rd switch (S3).

9. drive circuit as claimed in claim 1, is characterized in that the combination that described filter circuit comprises any one or capacity cell and inductance element in capacity cell or inductance element.

10. drive circuit as claimed in claim 1, is characterized in that described dim signal generator is according to the controlled signal of cut Voltage-output parameter after rectification.

11. drive circuit as claimed in claim 10, is characterized in that the controlled signal of described output parameter is pulse width modulating signal or amplitude controlled signal.

12. a light fixture, this light fixture possesses drive circuit as claimed in claim 1.